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Abstract

Background: Decreases in buccal microcirculation are associated with severity and outcomes of circulatory shock. However, there is evidence that cerebral function is unimpaired after even severe states of hemorrhagic shock. We therefore hypothesized that in severe states of hemorrhagic shock with profound decreases in buccal microcirculation, the cerebral microcirculation may be preserved.

Method: Craniotomies were performed in 15 male Sprague-Dawley rats, weighing 450–550g, to expose the parietal cortex for visualization of microcirculation. Animals were then bled via a catheter advanced into the descending aorta. An estimated 35% or 25% of blood volume was bled over 60 minutes and measurements were compared with unbled control. Sixty minutes after onset of hypotension, bled animals received normal saline infused over 30 minutes in amounts equivalent to two times the volume of shed blood. Cerebral and buccal microcirculations were visualized with orthogonal polarization spectral imaging.

Result: Reductions in mean arterial pressure (MAP) were partially reversed after fluid infusion (Figure 1⇓). Buccal microcirculation was restored to baseline level after the 25% blood loss and partially restored after the 35% loss. The cerebral microcirculation, however, was unchanged during both hemorrhagic hypotension and following volume repletion.

Conclusion: In contrast to the striking reduction in arterial pressure and systemic microcirculation, the cerebral microcirculatory blood flow was preserved during hemorrhagic shock of moderate and severe degrees. These findings confirm a dissociation between the macrocirculation and the cerebral microcirculation.